The rudiments of phenotypic change which describe malignancy have been defined in general, yet the underlying mechanisms of these changes in breast cancer remain to be fully elucidated. As the basis of these phenotypic changes arise from nuclear regulation, transcription and translation of proteins, a clearer characterization of these changes is needed, both in the malignant and benign phenotypes. The direct study of tissue samples obtained from the human breast specimens could provide a better basis for such understanding.